Sintered alloy having wear resistance at high temperature

ABSTRACT

The present invention relates to sintered alloys having wear resistance at high temperature composed of 5 to 15 percent tin and 4 to 25 percent chromium, the balance being copper, and the alloy being sintered to more than 88 percent of theoretical density ratio.

United States Patent 1 Niimi et a1.

[4 1 Dec. 4, 1973 SINTERED ALLOY HAVING WEAR RESISTANCE AT HIGH TEMPERATURE [76] Inventors: Itar Niimi, 4-1205, Obasama, Aza,

Takabari, Ooaza, Idaka-sho, Nagoya City; Kametaro Hashimoto, 29, 5-chome, Takami-cho, Toyota City; Kenzi Shitani, 3-38, 4-chome, Maruyama-cho, Toyota City; K0 Ishihara, 58-79, Kitayama, Ichiki, cho, Toyota City; Yoichi Serino, 2-1, Ekakushin-machi, Toyota City; Seishu Mitani, 11-5, I-Iigashi-machi, Anshubaba, Kyoto City; Kunim Imanishi, 2-11, Toei-cho, Mizuho-ku, Nagoya City, all of Japan 22 Filed: Aug. 17, 1971 [21] Appl. No.: 172,402

[30] Foreign Application Priority Data Dec. 28, 1970 Japan 45/120197 [52] US. Cl. 29/182, 29/l56.7 A, 75/200,

75/214 [51] Int. Cl. B22p 3/16, C22c 9/00 Primary Examiner-Carl D. Quarforth Assistant Examiner-R. E. Schafer Attorney-Arthur G. Connolly et al.

[ ABSTRACT The present invention relates to sintered alloys having wear resistance at high temperature composed of 5 to 15 percent tin and 4 to 25 percent chromium, the balance being copper, and the alloy being sintered to more than 88 percent of theoretical density ratio.

2 Claims, 1 Drawing Figure SINTERED ALLOY HAVING WEAR RESISTANCE AT HIGH TEMPERATURE BACKGROUND OF THE INVENTION The present invention relates to a sintered copper alloy having high anticorrosiveness and wear resistance athigh temperature, and more particularly to an alloy suitable for fabricating valve seats of the type used in internal combustion engines that use lead-free gasoline as fuel. Cast iron, heat resisting steel, and copper alloys and the like have been heretofore used as the principal materials for valve seat constructions. However, these materials have the disadvantage that through theuseof lead-free gasoline as fuel, the lubricating action of the lead: is lost and the wearing away of the valve seat is thereby remarkably increased. The engine output decreases to the extent that these materials are not feasiblefor fabricating valve seats.

The inventors of the present invention have made numerous studies for ameliorating the disadvantage mentioned above to obtain a sintered alloy having high heat conductibility and wear resistance at high temperature. The inventors found thata sintered alloy in which chromium (Cr) has been dispersed in a block-like state in a matrix of copper (Cu) and tin (Sn), and which contains copper as the principal constituentand to percent tin and 4 to 25 percent chromium, both by weight percent, and which has been sintered to more than 88 percent of theoretical density ratio, is extremely suitable for the purpose.

SUMMARY OF THE INVENTION The presentinvention relates to sintered copper alloys having excellent anticorrosiveness and wear resistance at high temperature'These alloys are most suitable for fabricating valve seats used in internal combustion engines.

The alloys according to the present invention are sintered alloys having wear resistance at high temperature, each characterized by containing 5 to 15 percent tin and 4 to 25 percent chromium, the balance being copper, and the alloy being sintered to more than 88 percent of the theoretical density ratio.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is a microscopic photograph showing the composition of an alloy according to the present invention, the matrix being a copper-tin alloy, and the block-like portion being chromium.

DETAILED DESCRIPTION OF THE INVENTION The sintered alloys according to the present invention are alloys in which chromium is dispersed in a block-like state in a matrix of copper and tin, as shown in the microscopic photograph of the drawing. Each alloy of the invention is characterized by containing copper as the principal constituent, and by weight percent, 5 to 15 percent tin and 4 to 25 percent chromium. Each alloy is sintered to more than 88 percent of the theoretical density ratio.

The sintered alloys according to the present invention have excellent thermal conductibility and wear resistance at high temperature. They are particularly suitable for valve seat constructions where lead-free gasoline is used; Also, these alloys are very suitable as valve seat materials for engines that use LPG (liquefied propane gas) as fuel where working conditions are more difficult than in the case where leaded gasoline is used. Also, the alloys may be used to fabricate bearings, especially in cases where the bearings are exposed to high temperatures or may reach high temperatures.

The effect and the reason for each constituent element of the alloy according to the present invention are as follows.

Among the constituents of the sintered alloys according to the present invention, copper-tin is well known as sintered bronze, and has long been used as a bearing material. In this constituent, tin is one which is added in order to ameliorate the mechanical strength and the wear resistance of the alloy. However, when the tin content is less than 5 percent, its effect is inferior, and when it becomes more than 15 percent, the mechanical strength of the alloy decreases considerably. Also, the capacity for holding chromium lowers as well. Thus, the tin content has been determined to be from 5 to 15 percent.

Chromium does not lower the hardness of the alloy even at high temperature. It forms chromium oxide at high temperature, and tends to lower the friction coefficient and thereby increase the wear resistance of the alloy. However, when the chromium content is less than 4 percent, its afiect on the alloy is inappreciable, and when it isincreased up to 35 percent, although it ameliorates the wear resistance, it tends to lower the strength of alloy. Therefore, the content of chromium has been determined as up to 25 percent.

With regard to the density of the alloy, when it is less than 88 percent of the theoretical density within the above-mentioned composition range, the heat radiation effect at high temperature is also inferior, and permanent strain occurs which makes the alloy unusable. This is the reason why the density has been determined as to be more than 88 percent.

In the sintered alloys according to the present invention hard chromium having excellent wear resistance at high temperature is dispersed in a block-like state in a comparatively soft matrix of copper-tin, which has good thermal conductivity, excellent wear resistance and anticorrosiveness. Appropriate material strength consists of two phases, hard and soft, and is particularly excellent in wear resistance at high temperature. Further, the increase of density of the alloys contributes to the increase of thermal conductibility at high temperature under high load and the prevention of permanent strain as well.

The sintered alloys according to the present invention, having the characteristics mentioned above, are extremely suitable for valve seat materials used in internal combustion engines, and more suitable for internal combustion engines using lead-free gasoline of LPG as fuel. These alloys are also suitable as bearing materials for hot rollers, for example. Further the constituent materials and the manufacturing process according to the present invention are extremely simple, with the advantage that the maintenance of quality is easily achieved even under mass production techniques.

The present invention is described below with reference to examples.

EXAMPLE 1 Electrolytic copper powders of under mesh. pulverized tin powders of under 100 mesh, and electrolytic chromium powders of under 200 mesh, are blended and mixed in a manner that they have a weight percentage consisting of 76 percent copper, 12 percent tin and 12 percent chromium. Thereafter, the powders are formed into a body having a density of 7.3g/cm under a forming pressure of 5 t/cm Then, the formed body is sintered at 860C. during one hour in a neutral gas atmosphere, and the sintered body is compressed again under a pressure of 7 t/cm to increase the density up to 7.9 g/cm. The product is a sintered alloy according to the present invention.

EXAMPLE 2 The same powders of Example 1 are blended in a manner that they have a weight percentage of 84 percent copper, 8 percent tin, and 8 percent chromium. After mixing the powders, the mixture is formed under a pressure of 5 t/cm into a body having a density of 7.3 g/cm. The formed body is sintered in a reducing gas atmosphere at 860C. during one hour, and the sintered body thus obtained is compressed again under a pressure of 7 t/cm to increase its density up to 8.1 g/cm. The product is a sintered alloy according to the present invention.

The following test results regard the properties and wear resistance of the alloys obtained by the methods of Examples 1 and 2, and those of conventional alloys.

TABLE Type of alloy Percentage Tensile Hardness Degree of constituent strength Hv (0.2) of wear (weight percent) ltg/mm (mm) Present Invention Example 76Cu-l2 l Sn-lZCr 400-450 0.50

(Blocklike Cr) I20 (matrix) Example 84Cu-8Sn 25 400-450 0.81 2 -8Cr (Blocklike Cr) 103 (matrix) Control Test Specimen Special Fe-3.5C- 40 250-300 5.38 cast 2.5Si-l Mn iron -0.5P-0.5Cr

-O.5Mo0. l V Cast 50Fe- 187 4.75 alloy 50Cu In the table, the wear quantity is expressed by the quantity of wear in millimeters in the direction of height of the specimen after it has been subjected to a test on a so-called sliding high cycle impact tester having a mechanism in which an angular specimen fixed in an aluminum alloy is rotated 10 times in a minute at a high temperature of from 450 to 500 C. Also, 2,500 times percussion per minute are applied with a surface pressure of 10 kg/cm by means of a jig made with a heat resisting steel.

What is claimed is:

l. A sintered alloy having wear resistance at high temperature consisting essentially of 5 to 15 percent by weight tin, 4 to 25 percent by weight chromium and the balance copper with the chromium dispersed in a block-like state in a matrix of copper and tin, and the alloy being sintered to more than 88 percent of theoretical density ratio.

2. A valve seat of an internal combustion engine fabricated of the alloy according to claim 1. 

2. A valve seat of an internal combustion engine fabricated of the alloy according to claim
 1. 